U.S. President Donald Trump signs a proclamation on adjusting imports of steel into the United States next to steel and aluminum workers in the Roosevelt Room of the White House in Washington, D.C., U.S., on Thursday, March 8, 2018.

Photo: Andrew Harrer, Bloomberg

President Trump doesn’t care about the opinions of his top economic adviser, his party’s leadership or a string of global allies. He’s plowing through the chaos he’s created by slamming down tariffs on foreign steel and aluminum.

After a week of confusion and worry, the president is tempering his first-blush idea to punish all foreign imports of the two metals. He’s leaving out Canada and Mexico for now and possibly Australia. Other producers, including China, could get off the tariff list if they change export practices subject to presidential review.

But softening a bad idea doesn’t make it better. The specifics remain hazy, though not the upshot: An unpredictable president is going his own way, bouncing between tough talk and half-formed compromises. He remains as unsettled and untrustworthy as ever.

His thought process isn’t the only issue. The notion of import tariffs imposed by the world’s biggest trading nation has enormous impacts. His top economic adviser, Gary Cohn, is quitting over the move, which could bring on a trade war as other countries throw up barriers in response.

Trump is promising to be “flexible” in imposing the import levies, suggesting he might drop other nations as events proceed. That only adds to the uncertainty he’s created on a topic that worries allies wondering about Washington’s direction.

Tariffs are a crowd-pleaser in Rust Belt regions where mills have closed, an aspect he played up by surrounding himself with union workers at a White House signing ceremony. But it’s also theater possibly designed to shift attention from the investigation over possible electoral collusion with Russia and a messy payoff to a porn star linked to Trump.

On trade imbalances, the answer isn’t import levies that will drive up consumer costs, hurt industries that use steel and aluminum, and curtail American exports. A serious solution needs to come from the political consensus he’s shattering. Reworking the rules on global trade can’t be done with this president’s signature. Trade agreements, not import walls, are the way to go in a globalized business world.

Trump is breaking with a decades-long consensus in both parties that favors free trade. Offending countries should face sanctions but not on the sweeping scale Trump is threatening. The doctrine of free trade is especially prized by Republicans, who are stunned to discover their party leader isn’t with them on a basic principle.

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“We urge you to reconsider the idea of broad tariffs to avoid unintended negative consequences,’’ said 100 Republican lawmakers in a letter to Trump. In brushing off that warning, the president is isolating himself from reality — along with his most important potential allies, domestic and foreign.

This commentary is from The Chronicle’s editorial board. We invite you to express your views in a letter to the editor. Please submit your letter via our online form: SFChronicle.com/letters.